An investigation is underway surrounding Mikey’s death, as well as pending autopsy results.

Mikey left Weezer shortly after the release of the band’s Green Album in 2001 which featured the hit “Hash Pipe,” one of the biggest tracks ever for the group.

He left to pursue art and develop his prowess as a painter.

Weezer released the following statement on the band’s website: “It saddens me and the guys in Weezer so much to say that our beautiful, creative, hilarious and sweet friend Mikey Welsh has passed away at the very young age of 40. A unique talent, a deeply loving friend and father, and a great artist is gone, but we will never forget him. His chapter in the Weezer story (’98 – ’01) was vital, essential, wild, and amazing.”

Weezer played its scheduled show during Chicago’s RIOTfest on Sunday, dedicating the concert to Mikey.